1. Field of the Invention
This invention relates in general to coatings applied by physical vapor deposition, and in particular to a new and useful large or small cathodic arc source design for reliable operation and uniform cathode erosion.
2. Brief Description of the Prior Art
Many prior configurations of cathodic arc sources have been designed. In all of these, it has been desirable to confine the arc to the target surface, and obtain uniform erosion. Some of the prior designs, such as U.S. Pat. No. 3,793,179 to Sablev, employ magnetic fields to confine and steer the arc along the usable target material, but result in non-uniform target erosion. These designs, however, do not work with magnetic target materials. Some system, such as U.S. Pat. No. 4,559,121 to Mukri, utilize either insulating or conducting rings around the edges of the target to confine the arc. These systems break down, or allow the arc to jump to conducting surfaces behind the target. Additionally, these systems require maintenance, as well as result in larger cathodes that require more room in the coating system. With either metal or ceramic rings around the edges of the target, only part of the total assembly area produces the vaporized coating material. U.S. Pat. Nos. 4,929,322 to Sue et al and 3,783,231 to Sablev only allow very small cathodes, thereby limiting their usefulness and requiring many units for a large production coating system. In U.S. Pat. No. 3,836,451 to Snaper, a beam gun is disclosed to direct a beam of particles onto the substrate.
With the present invention, all of the assembly area is active and is available to produce the coating material. By placing the insulator ring below, and spaced from the target, the arc is prevented from leaving the cathode, by eliminating any possible path. The inside surfaces of the insulator are well baffled to prevent coating and prevent arc conduction behind the insulators. The arc cannot enter the small gap between the insulator and the bottom cantilevered edge of the target.